A precombustion-chamber gas engine is used as one of engines for electricity generation or the like. The precombustion-chamber gas engine includes a main combustion chamber defined between a piston, a liner, and a cylinder head and a precombustion chamber communicating with the main combustion chamber through a nozzle to allow the following combustion workflow.
Firstly, ignition fuel gas (fuel gas or rich mixed gas) is supplied to the precombustion chamber from a supply line for ignition fuel gas. Secondly, in a compression stroke, lean air-fuel premixture in the main combustion chamber flows into the precombustion chamber through a nozzle, and the lean premixed gas is mixed with the ignition fuel gas in the precombustion chamber so that a stoichiometric mixture ratio (stoich) is achieved immediately before ignition. Then, a spark plug sparks in the precombustion chamber, and flame propagation combustion occurs in the precombustion chamber. Combustion gas generated in the precombustion chamber is injected as a torch into the main combustion chamber through the nozzle to combust the mixed gas in the main combustion chamber by torch combustion and flame propagation combustion.
The above-described precombustion-chamber engine allows the lean premixed gas in the main combustion chamber to combust at a relatively low temperature and thereby reduces the generation of NOX or the like, resulting in low pollution. Further, even when the main combustion chamber contains the lean premixed gas, combustion can be quickly completed in the main combustion chamber because of the injected torch with enough energy.
Besides, the mixture state of the ignition fuel gas and the lean premixed gas in the precombustion chamber is significantly affected by combustion fluctuation (i.e. change of combustion state in each cylinder among combustion cycles) in the main combustion chamber. A reduction in combustion fluctuation contributes to improvement of engine efficiency, and thus, engine efficiency can be improved by facilitating mixing of the ignition fuel gas with the lean premixed gas in the precombustion chamber to homogenize the air-fuel mixture in the precombustion chamber.
Patent Document 1 discloses a precombustion-chamber engine which aims at suppressing the occurrence of abnormal combustion such as pre-ignition. This precombustion-chamber gas engine includes a precombustion chamber composed of a precombustion-chamber space part provided with an ignition plug and a precombustion-chamber communication passage provided with a nozzle, in which the precombustion-chamber space part is eccentrically disposed with respect to the central axis of the precombustion-chamber communication passage. This structure causes a regular gas flow in the precombustion chamber to homogenize the air-fuel mixture, thereby suppressing the occurrence of abnormal combustion.